testing: adding glFlush() each frame for performance testing

indra/llwindow/llwindowmacosx.cpp

@@ -1273,6 +1273,7 @@ BOOL LLWindowMacOSX::setSize(const LLCoordScreen size)
 
 void LLWindowMacOSX::swapBuffers()
 {
+	glFlush();
 	aglSwapBuffers(mContext);
 }
 

indra/llwindow/llwindowsdl.cpp

@@ -984,7 +984,10 @@ BOOL LLWindowSDL::setSize(const LLCoordScreen size)
 void LLWindowSDL::swapBuffers()
 {
 	if (mWindow)
+	{	
+		glFlush();
 		SDL_GL_SwapBuffers();
+	}
 }
 
 U32 LLWindowSDL::getFSAASamples()

indra/llwindow/llwindowwin32.cpp

@@ -2858,6 +2858,7 @@ BOOL LLWindowWin32::resetDisplayResolution()
 
 void LLWindowWin32::swapBuffers()
 {
+	glFlush();
 	SwapBuffers(mhDC);
 }